American Indian (Al) children are at elevated risk for experiencing poverty, parental mental health disorders, household exposure to substance use, domestic violence, and maltreatment, all of which increase their risk of developing mental health and substance use problems as adolescents and adults. Very few programs designed to meet their needs within their own tribal communities and consistent with Ai cultural practices exist, and even fewer are based on evidence from high-quality randomized trials. Considerable research points to the importance of caregiver sensitivity and responsiveness in developing secure infant attachment. This proposal aims to implement a theoretically driven, relationship-based intervention strategy: Promoting First Relationships (PFR). PFR promotes trusting and secure caregiver-child relationships and healthy child development, and several studies have shown the positive effects of PFR for at-risk populations. Via collaborations with two tribal partners, we will adapt PFR to Al contexts and deliver the PFR intervention and test its efficacy in a randomized, controlled trial with a wait-list control group. Our primary purpose is to test the efficacy of PFR in improving caregivers' sensitivity and responsiveness to their young children and enhancing children's social and emotional outcomes, especially their attachment security with caregivers. We aim to (1) test the feasibility and effectiveness of training community service providers in the use of PFR by measuring pre- and post-training service provision strategies and interactions with caregivers and infants and (2) assess the extent to which the PFR group, compared with controls, demonstrates improvements in caregivers' sensitivity and responsiveness and children's social and emotional competencies and attachment security. There is a critical need for effective primary prevention interventions aimed at Al children who grow up under stressful circumstances. By promoting sensitive caregiving and child attachment security, we can minimize the impact of contextual stressors on children and Improve their risk outlook. Our community-based methods and perspectives will strengthen our partners' support for the PFR program, contribute to its sustainability, and mitigate against mistrust of the research enterprise.